An electric power steering device includes a motor for generating a steering assist torque that assists a steering operation of a steering wheel, and an electronic control unit (hereinafter referred to as “ECU”) for controlling the energization of the motor. The ECU includes a motor drive circuit formed of switching elements, a microcomputer for calculating a control amount of the motor so as to generate a target assist torque corresponding to a steering torque, and a switch drive circuit for outputting a PWM-controlled gate signal to the switching elements of the motor drive circuit in accordance with the control amount calculated by the microcomputer.
This kind of electric power steering device prevents the motor and the motor drive circuit from being damaged by heat generation in a manner that detects temperatures thereof and limits a current to be supplied to the motor when the detected temperature exceeds a threshold set for overheat prevention. In an electric power steering device proposed in Patent Literature 1, the temperature of the switch drive circuit is detected as well, and the current to be supplied to the motor is limited when any one of the temperatures detected from the motor drive circuit and the switch drive circuit exceeds a threshold set for each circuit.